Method of making tubes of pyroxylin material or the like



June 9, 1942. J. N. WHITEHOUSE 2,236,045 METHOD OF MAKING TUBES OFPYROXYLIN MATERIAL OR THE LIKE Filed D60. 2, 1959 INVENTOR J'Smv Mwm-renouse Y ATTO R N EYS Patented June 9, 1942 2 UNITED STATES PATENTOFFICE METHOD OF MAKING TUBES OF PYROXYLIN MATERIAL OR THE LIKE 2Claims.

This invention relates to the manufacture of tubes, such as are used inmaking the barrels of fountain pens, from pyroxylin or otherthermoplastic material. However such tubes are made, e. g., from aspiral wound strip, from a strip folded and with longitudinal edgesbuttwelded, from a cylindrical block, etc., they require a polishingoperation on the exterior, in order that the finished article maypresent the desired attractive appearance. Heretofore the tube, prior tothe polishing operation, has been so rough and irregular as to itsexterior surface that an expensive and wasteful grinding operation wasrequired.

Where the tube was made by bending the strip into tubular shape and thendrawing it through a metal tube of such interior diameter that thelongitudinal edges of the pyroxylin tube were in contact, softening thepyroxylin material and applying a suitable cementing agent along theabutting edges. the resulting pyroxylin tube has been irregular ingeneral cross section, rough and irregular as to its exterior surface,and with a prominent seam-projection extending longitudinally of theexterior surface.

By my invention it is proposed to form a tube of the pyroxylin materialas by the butt-welding method, softening the tube as by immersing it inhot water, then inserting a closely fitting unyielding truly cylindricalmandrel into the tube and thereafter hammer-molding the tube in such away and under such conditions of temperature interiorly and exteriorlyof the tube that the tube emerges from the operation in trulycylindrical form, with the exterior surface substantially free fromirregularities and undesirable projections, and with a densification ofthe wall of the tube at and to an appreciable distance below theexterior surface. And as a result of this treatment the exterior of thetube requires a minimum of final polishing, and the polishing isfacilitated and improved because of the densification referred to.

In the accompanying drawing, which is to be taken as a part of thisspecification,

Fig. 1 is a more or less diagrammatic showing of a tube in its relationto the supporting mandrel and to the hammer-molding elements involved inthe carrying out of my process;

Fig. 2 illustrates a section of tubing which has been formed by theso-ca1led butt-welding method, and without being subjected to m process; and

changes have occurred in the shape, etc. of the tube after it has beensubjected to my process.

Referring to the numerals on the drawing, and first to Fig. 2, let it beunderstood that a tube indicated at 4 has been made by bendin a strip ofpyroxylin material of suitable width into tubular form with the edges ofthe strip substantially abutting. This so-formed tube, it will beassumed, has been drawn through a metal tube with the edges thereby heldin the abutting relation, and while being so drawn heat has been appliedand/or a cementing material effective at the abutting edges, so thatthese are substantially united. All this has taken place in the absenceof interior support for the pyroxylin tube. I have found that theresulting pyroxylin tube is apt to depart extensively from truecircularity, that its exterior surface exhibits a marked seam-projectionat the united edges, indicated at 5 in Figs. 1 and 2, and that whereheat was employed as a preliminary to or during the forming operation,as is usually the case, the material of the tube is in an expandedcondition so that a polishing operation performed on it does not havethe maximum effectiveness. There are also apt to be irregularities,whether by way of projections or depressions, in the remaining exteriorand interior surfaces other than the seam-projection, suchirregularities being indicated at 6 in Figs. 1 and 2.

Starting with such a tube as I have just described, according to myinvention I first insure that it is in a relatively soft condition, asby immersing it in hot water; I then insert into it a cylindricalmandrel such as is indicated at I in Fig. 1, the mandrel being of suchcross sectional dimensions that the tube is snug on it and brought toapproximate circularity, except for such surface irregularities as mayexist, particularly the seam-projection 5 and the irregularities 6. Thetube may be of any convenient length, and for ease in handling, themandrel may project beyond both ends of the pyroxylin tube. The mandrelis heated to a degree sufficiently to keep the pyroxylin materialrelatively soft. The tube and the supporting mandrel are nowprogressively advanced between the members 8 and 9 of a hammer-moldingassembly, these members 8 and 9 being at a relatively lower temperaturethan the temperature of. the mandrel or of the tube, so that as themembers 8 and 9 operate upon the tube, as hereinafter described, theywill have a chilling effect upon the exterior of the tube. Thetemperature of the elements 8 and 9 need not be much below atmospheric,

but at any rate it is desirable to have a considerable temperaturedifferential between the mandrel and the elements 8 and 9, whichdifferential can be maintained in any suitable way during thehammer-molding operation. The elements 8 and 9 are manipulated in anypreferred way, preferably mechanically, so that they move intermittentlytowards and from each other in the hammer-molding operation, opposedfaces of the elements 8 and 9 being cavitated as at H! so that when thetube and mandrel are first inserted, the cavitations closely fit aroundthe exterior of the tube, while the opposed faces of the members 8 and 9on either side of the cavitations H] are spaced apart somewhatas shownin Fig. l. The effect of movement of the members 8 and 9 towards eachother is to mold and hammer the exterior surface of the tube, graduallydensifying and reducing the wall thickness thereof until such time asthe opposing faces of members 8 and 9 on either side of the cavitationsH] are in contact, at which time the cavitations It! will together forma complete cylinder closely encompassing the tube, which, by reason ofthe hammer-molding and incidental exterior chilling, will have beendensified to an appreciable depth from the exterior inwardly, and whoseexterior surface will have been made smooth and uniform, with theremoval of undesirable projections such as those indicated at 5 and 6.The advance of the mandrel and tube through the hammer-molding assemblyis progressive, and while it is going on relative rotation between themandrel and tube on the one hand, and the hammer-molding assembly on theother hand, properly synchronized with the movements of approach andseparation of the hammer-molding elements, and with the stepby-stepforward movements of the mandrel and tube, is effected, with obviousresults. This relative rotation may be accomplished by intermittentpartial step-by-step rotation of the mandrel and tube, while the members8 and 9 are held against rotation relatively to the mandrel and tube; orthe hammer-molding assembly :may be given a step-by-step rotationsuitably synchronizedwith the movements of the elements 8 and 9 towardsand from each other, the mandrel and tube being held against rotation.It will be appreciated that the full length of the tube is not operatedupon simultaneously, but it is advanced progressively and with someuniformity of timing synchronized with the movements of thehammer-molding elements, so that when the operation is complete, everyportion of the length will have been operated upon, that is to say,hammered and molded and densified to substantially the same extent, sothat the finished tube will be uniform throughout. The mandrel will, ofcourse, be withdrawn from the tube.

The result of the operation above described is a tube, such as isillustrated in Fig. 3 and at the right-hand end of Fig. 1, which istruly circular inside and out, whose exterior surface in particular issmooth and uniform and free from undesirable irregularities orprojections, and which is desirably densified from the exterior to anappreciable depth of the wall thickness. Such a tube requires nogrinding and but little polishing, and the polishing is the moreeffective because of the densification at the exterior of the tube.

I claim:

1. The method which consists in providinga tube of pyroxylin materialwith a relatively heated interior supporting mandrel, advancing the tubeand mandrel progressively through the field of operation of a relativelycool hammer-molding assembly and causing relative step-by-step rotationbetween the mandrel and tube on the one hand and the hammer-moldingassembly on the other hand.

2. The method which consists in providing a softened tube of pyroxylinmaterial with a relatively heated interior supporting mandrel, advancingthe tube and mandrel progressively through the field of operation ofarelatively cool hammer-molding assembly and causing relativestep-by-step rotation between the mandrel and tube on the one hand andthe hammer-molding assembly on the other hand.

JOHN N. WHITEHOUSE.

